1. Field of the Invention
The invention relates to an electric motor drive, having an electric motor that is triggerable via an end stage.
2. Prior Art
Electric motor drives of this generic type are known. They are used for instance in motor vehicles, as control motors. They are then operated at a supply voltage furnished by a motor vehicle battery. The electric motors embodied as direct current motors can be used in thermally critical areas of the motor vehicle, such as in the immediate vicinity of an internal combustion engine, among other areas. It is also known to provide electric motor drives with an overload protection that is intended to protect the electric motors against irreparable thermal damage, for instance if sluggishness suddenly occurs.
To protect electric motors against thermal overload, it is known to detect a housing temperature and/or an armature winding temperature of the direct current motor via a temperature sensor or a bimetallic element. The electric motor is rendered currentless if a permissible temperature is exceeded.
It is also known for electric consumers, such as motor end stages for direct current motors in motor vehicles, to be triggered with a pulse-width modulation signal. The electric consumer is connected to a voltage source or disconnected from the voltage source in accordance with a duty factor of the pulse-width modulation signal.
From International Patent Disclosure WO 94/27349, an electric motor drive is known in which a motor end stage is connected to a trigger circuit, and the trigger circuit generates an overload signal as a function of a temperature of the electric motor. A temperature of the electric motor can be calculated here from a power loss, or a variable proportional to it, on the basis of measured motor data during the duty cycle of the electric motor and integrated; for forwarding the overload signal, the integration value is compared with a predeterminable threshold value. A disadvantage here is that the requisite measurement of motor data during the duty cycle of the electric motor dictates effort and expense for measurement that moreover involves error, so that an exact overload signal cannot be ascertained.